[gcc(refs/vendors/ibm/heads/gcc-10-branch)] libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282)

[gcc(refs/vendors/ibm/heads/gcc-10-branch)] libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282)

[Peter Bergner]

https://gcc.gnu.org/g:161fb9dfc886afb70dcfb45a51571df5e3fce9eb

commit 161fb9dfc886afb70dcfb45a51571df5e3fce9eb
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed May 27 22:55:21 2020 +0100

    libstdc++: Strip cv-qualifiers in std::atomic<FP> (PR 95282)
    
    This squashes two commits, r11-674 and r11-1401.
    
            PR libstdc++/95282
            * include/bits/atomic_base.h (__atomic_impl::load): Add
            const-qualifier to parameter so that _Tp is deduced as the
            non-const type, and use _Val to get the unqualified type.
            (__atomic_impl::exchange): Use the _Val alias to remove
            volatile from the reinterpret_cast result type.
            * testsuite/29_atomics/atomic_float/95282.cc: New test.
    
    (cherry picked from commit e40b11a91cb345db1324c3cb8f75b01e28056693)

Diff:
---
 libstdc++-v3/include/bits/atomic_base.h            | 10 +++----
 .../testsuite/29_atomics/atomic_float/95282.cc     | 35 ++++++++++++++++++++++
 2 files changed, 40 insertions(+), 5 deletions(-)

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 87fe0bd6000..41d5928e482 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -850,21 +850,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { __atomic_store(__ptr, std::__addressof(__t), int(__m)); }
 
     template<typename _Tp>
-      _GLIBCXX_ALWAYS_INLINE _Tp
-      load(_Tp* __ptr, memory_order __m) noexcept
+      _GLIBCXX_ALWAYS_INLINE _Val<_Tp>
+      load(const _Tp* __ptr, memory_order __m) noexcept
       {
 	alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
-	_Tp* __dest = reinterpret_cast<_Tp*>(__buf);
+	auto* __dest = reinterpret_cast<_Val<_Tp>*>(__buf);
 	__atomic_load(__ptr, __dest, int(__m));
 	return *__dest;
       }
 
     template<typename _Tp>
-      _GLIBCXX_ALWAYS_INLINE _Tp
+      _GLIBCXX_ALWAYS_INLINE _Val<_Tp>
       exchange(_Tp* __ptr, _Val<_Tp> __desired, memory_order __m) noexcept
       {
         alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
-	_Tp* __dest = reinterpret_cast<_Tp*>(__buf);
+	auto* __dest = reinterpret_cast<_Val<_Tp>*>(__buf);
 	__atomic_exchange(__ptr, std::__addressof(__desired), __dest, int(__m));
 	return *__dest;
       }
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc b/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc
new file mode 100644
index 00000000000..2de751c6ad4
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_float/95282.cc
@@ -0,0 +1,35 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <atomic>
+
+float
+test01()
+{
+  std::atomic<float> a;
+  return a.load();
+}
+
+float
+test02()
+{
+  volatile std::atomic<float> a;
+  return a.load();
+}